Update PyPI mirror for sqlalchemy-migrate releases

* modules/openstack_project/files/zuul/layout.yaml: After each
sqlalchemy-migrate release is uploaded to pypi.python.org,
immediately run the post-mirror jobs to update pypi.openstack.org so
it will be reflected there as well.

Change-Id: I34c747cf1ecbc923e5db9c53a5766b388f51e33b
Merge "Update PyPI mirror for sqlalchemy-migrate releases"